1. Field of the Invention
The present invention relates to a method and a device for treating waste liquid, solvent separator and a cleaning or a dry cleaning device using the device or the separator. More specifically, the present invention relates to a method and a device for treating a waste liquid by which a chlorine containing organic solvent present in the exhaust gas or waste liquid generated during a process using a chlorine containing organic solvent, such as trichloroethylene used in a metal part washing device, or tetrachloroethylene used in a dry cleaning device, is selectively separated, decomposed by a photocatalyst, and made harmless. The present invention also relates to a solvent separator which may be used for selectively separating/collecting an organic solvent containing chlorine from a waste liquid, and a cleaning or a dry cleaning device using such a device or solvent separator. The solvent separator of the invention possesses an excellent processing efficiency.
2. Description of Related Art
Chlorine containing organic solvents have been widely used because they are excellent cleaning agents due to their superior cleaning properties, stability, and non-flammability.
Recently, since the chlorine containing organic solvents are considered to be hazardous air pollutants and designated as the priority controlled substances, self-regulated substances, etc., in air pollution control laws, various attempts have been made, such as one utilizing an adsorption method using activated carbon or a heat vaporization treatment method, to decrease the amount of chlorine containing organic solvents contained in the waste liquid or exhaust gas discharged from cleaning devices, such as dry cleaning devices, to within the emission standard value (for example, 0.1 mg/L of tetrachloroethylene in Japan) defined in the Water Pollution Control Law.
In an adsorption method using activated carbon, it is necessary to replace the activated carbon when the adsorption capacity of the activated carbon is saturated. However, it is difficult to determine when the activated carbon has lost its adsorption capacity. Also, it is necessary for the user to dispose of the adsorption-saturated activated carbon as designated waste, or to recycle it after subjecting it to a desorption-regeneration process using water vapor. Accordingly, the use of activated carbon is inefficient and gives rise to extra costs.
On the other hand, by using a heat vaporization treatment method, the concentration of chlorine containing organic compounds in waste liquid can be decreased to within emission standard values by vaporizing the waste liquid.
However, according to this method, there is the problem that the treatment efficiency is decreased when the concentration of the chlorine containing organic compounds in waste liquid is low. Also, since the vaporized chlorine containing organic compounds are emitted to the air without being decomposed, there is a problem that the amount of chlorine containing organic compounds in the exhaust gas discharged in the environment cannot be substantially controlled.
Also, since regulations relating to the emission of chlorine containing organic compounds have been made increasingly stringent, there is demand for a method and a device for treating waste liquid having an excellent decomposition efficiency.
In addition, since water is usually contained in the waste liquid discharged from a cleaning device, such as a dry cleaning device, it is necessary to separate the water from the waste liquid in order to collect the chlorine containing organic solvent. Conventionally, methods in which the difference in specific gravity between a chlorine containing organic solvent and water is utilized to separate the chlorine containing organic solvent from water have been generally employed. When aqueous waste liquid containing water and a chlorine containing organic solvent is left to stand in a container, water and the solvent are separated in two layers and the chlorine containing organic solvent whose specific gravity is larger than water constitutes the lower layer. The chlorine containing organic solvent present in the lower layer is discharged and separated from the water.
However, if the chlorine containing organic solvent is dispersed and present in waste liquid in a fine particle state, it is difficult to achieve perfect separation of the solvent and some of the solvent remains in the water. Also, if the waste liquid is collected and addition and discharge of the waste liquid are carried out repeatedly in a recovery container, the chlorine containing organic solvent and water, which have been separated in two layers, are again mixed and dispersed, and then discharged in the dispersed state. Accordingly, by using a conventional separation method which utilizes the difference in specific gravity between a chlorine containing organic solvent and water, it is not possible, or at least difficult, to decrease the concentration of chlorine containing organic compounds in the waste liquid to a level satisfying the above-mentioned emission standards.
Moreover, since the laws for regulating discharge of the above-mentioned chlorine containing organic compounds are becoming increasingly stringent, there is a demand for a method and a device for treating waste liquid having a better separation efficiency have been awaited.
The present invention takes into consideration the above-mentioned circumstances, and has an object of providing a method for treating waste liquid in which a solvent separation process is incorporated in a series of processes for decomposing chlorine containing organic solvent present in waste liquid so that the treatment efficiency is improved and the emission of secondary by-products such as chlorine gas is decreased. The present invention also provides a device which is used for the above-mentioned method, and a cleaning or a dry cleaning device using the device for treating waste liquid, which are capable of automating the above-mentioned series of processes. In addition, the present invention provides a solvent separation device capable of selectively separating and collecting chlorine containing organic solvents, especially, finely dispersed chlorine containing organic solvents, contained in waste liquid with excellent processing efficiency.
The above objects may be achieved by a solvent separator including: an introduction member which introduces a mixture comprising chlorine containing organic solvent and water; a separation unit comprising a separation member made of a water-repellent and/or lipophilic porous material, which carries out the separation of the mixture; a water drainage member through which water separated by the separation unit is discharged; and a solvent drainage member through which the chlorine containing organic solvent separated by the separation unit is discharged.
The present invention also provides a solvent separator including: an introduction member which introduces a mixture comprising chlorine containing organic solvent and water; a separation unit comprising a separation member made of a water-repellent and/or lipophilic porous material, which carries out the separation of the mixture; a water drainage member through which water separated by the separation unit is discharged; a supply member which supplies air to the separation unit to vaporize the chlorine containing organic solvent; and an exhaust member through which the air supplied by the supply member and/or vaporized chlorine containing organic solvent is discharged.
In accordance with another aspect of the invention, the shape of the separation member is a film, plate, tube, container, or granules.
The present invention also provides a dry cleaning device including the above-mentioned solvent separator.
The above objects may also be achieved by a method for treating waste liquid including the steps of: carrying out a solvent separation process in which chlorine containing organic solvent present in the waste liquid is separated; carrying out a vaporization treatment process in which a part of the chlorine containing organic solvent remains in the waste liquid after the solvent separation process is vaporized; carrying out a photooxidation-decomposition process in which gases vaporized from the waste liquid are subjected to a photooxidation-decomposition treatment; and carrying out an after-treatment process in which decomposition product gases produced by the photooxidation-decomposition treatment are converted into a harmless substrate.
In accordance with another aspect of the invention, the decomposition product gases are adsorbed, and/or absorbed, and neutralized in the after-treatment process to be converted into a harmless substrate.
In yet another aspect of the invention, the solvent separation process is performed prior to the vaporization treatment process.
In yet another aspect of the invention, the waste liquid is made to contact a separation member made of a water-repellent and/or lipophilic porous member so that the chlorine containing organic solvent present in the waste liquid is adsorbed by the separation member in the solvent separation process.
In yet another aspect of the invention, the vaporization treatment process is performed by using an aeration method.
In yet another aspect of the invention, the vaporization treatment process further includes a step of vaporizing the chlorine containing organic solvent adsorbed by the separation member.
The above objects may also be achieved by a waste liquid treatment device, including: a solvent separation unit which separates chlorine containing organic solvent present in waste liquid; a vaporization treatment unit which vaporizes a part of the chlorine containing organic solvent which is not separated by the solvent separation unit and remains in the waste liquid; a photooxidation decomposition processing unit which photooxidizes and decomposes gases vaporized from the waste liquid by the vaporization treatment unit; an after-treatment unit which converts decomposition product gases produced by the photooxidation-decomposition processing unit into a harmless matter; and a control unit including a sequencer which controls an operation of the solvent separation unit, the vaporization treatment unit, the photooxidation decomposition processing unit, and the after-treatment unit.
In accordance with another aspect of the invention, the after-treatment unit adsorbs, and/or absorbs, and/or neutralizes the decomposition product gases in order to convert the decomposition product gases into a harmless substance.
The present invention also provides a cleaning device including the above-mentioned waste liquid treatment device.
The present invention also provides a dry cleaning device including the above-mentioned waste liquid treatment device.